This invention relates to an accumulator or pressure control device especially adapted for liquid dispensing systems, and particularly for water systems dependent upon well water, a pump and, because of intermittent use, an intermittent source of pressurization for the system. A simple prior art system for accommodating the pressurization of a well water system, for example in a dwelling, comprises a pipe extending into the underground water supply, a pump and a reservoir tank. Frequently, the tank is a metal container having no valve and in which air is merely trapped. In some installations, a valve, such as a regular tire valve, may be positioned at or near the top of the container and an outlet near the bottom. No diaphragm is provided. A charge of air is introduced into the tank, usually occupying about one-half the volume of the tank and to a pressure sufficient to force water into the plumbing system connected thereto. A pressure switch senses the pressure within the tank or in the water line, as the case may be, and operates between limits, for example between 20 and 40 psi. If the pressure falls below 20 psi, the pump is activated and continues to operate until the pressure in the system is built up to 40 psi, when the pump is turned off by the pressure switch.
Typical prior art accumulators include a pressure vessel having an inflatable bag therein, with an inflating valve extending through one end of the tank. An inlet and outlet aperture is provided in the other end of the tank, and that aperture is in fluid communication with the water system. As water is pumped into the tank, the bag is forced upwardly by the incoming water. This upward movement is characterized by a sharp annular crease adjacent the inner sidewall of the vessel, which progresses upwardly as the water rises and downwardly as the water is forced from the tank by the pressure in the bag. Thus, there is a substantially constant flexing of major portions of the sidewall of the bag.
Furthermore, in many prior art accumulator tanks the inlet-outlet strainer is domed and has drain openings spaced a substantial distance from the bottom of the tank. Grit tends to accumulate between the drain openings and the bottom of the tank which abrades the bag as the bag contacts these particles. The abrading action plus the annular flexure seriously limits bag life, necessitating frequent replacement of the bag.